Abstract: This paper describes how to use the fixcable drown type floating operational platform and non-dispersible concrete to concrete a large area stncture at 20m water depth. The technique of underwater concreting is also applied to concrete the thin layer. According to the testing results,it is proved that the underwater concreting strength conforms with the design requirements and the pictures photoed under water indicate that the comcreting surface is rather smooth and the height satisfies our clients.